In Dianetics, L. Ron Hubbard states that the purpose of the mind is to solve problems relating to survival.

The mind directs the individual in the effort of survival and bases its operations upon the information that it receives or records. The mind records data using what are called mental image pictures.

Such pictures are actually three-dimensional, containing color, sound and smell, as well as other perceptions. They also include the conclusions or speculations of the individual. Mental image pictures are continuously made by the mind, moment by moment. You can, for instance, examine the picture of what you had for breakfast this morning by recalling breakfast. And you can similarly recover a picture of an event that occurred last week by recalling it, or even recall something that happened much further in the past.

Mental image pictures are actually composed of energy. They have mass, they exist in space, and they follow some very, very definite routines of behavior, the most interesting of which is the fact that they appear when somebody thinks of something. For example, if a person thinks of a certain dog, he gets a picture of that dog.